This invention relates to an igniter for use on a gas turbine engine and, more particularly, the invention is concerned with providing an improved igniter in which vent passages in the vicinity of the electrode are placed in communication with the ambient environment external to the engine during ignition sequence so that fuel-air mixture abstracted from the engine will flow over the electrode, thereby enhancing the probability of ignition.
Heretofore, it has been common practice to provide igniters that extend into the combustion chambers of gas turbine and jet engines with openings through which ventilating or cooling air can be passed. Such cooling air is used to protect the igniter from damage during normal operation of the engine.
A gas turbine or jet engine is customarily started by causing the compressor section to be rotated at high velocity prior to the initial introduction of fuel so that the air flow within the engine assumes a normal working pattern. With ventilated igniters, this pattern provides for the passage of air through openings on the side of the igniter and along through the shell and out around the electrode where the initial spark is to occur. Starting problems have been encountered with these presently known igniters in most engines because the normal air flow pattern and velocity is sufficiently high to cause the fuel-air mixture to be blown away from the area where the spark occurs. When this happens, the probability of ignition is greatly diminished, especially when it becomes necessary to restart the engine after "flame-out."
Various attempts have been made to overcome the abovementioned drawbacks including, for example, closing off the working end of the igniter to prevent the cooling air from reaching the sparking tip during the ignition sequence. However, this effort did not prove successful because of the great increase in temperature of the igniter tip during operation and failure within a short time thereafter.
Thus it can be seen that it would be most desirable to provide a vented igniter that would be capable of operation under the most severe conditions without being subject to premature failure and would operate most consistently in an effective manner to start and/or restart the engine during a normal air flow pattern.